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Audio ICs

BA3884F / BA3884S

FCircuit operation

The BA3884F / S high-definition sound processor sys-

tem IC treats the amplifier and speakers as a total audio

system, and performs signal processing at the amplifier

input stage to accurately reproduce the rise sections of

audio signals that determine the characteristics of sound,

and ensure that the replayed audio is as close to the origi-

nal sound and as natural sounding as possible.

Problems relating to playback of sound on audio sys-

tems.

With naturally-generated sound, high-frequency har-

monic components generally occur first, followed by the

fundamental frequency components. This also applies to

the attack section of the sound that characterizes many

musical instruments. It is the amplitude component that

gives form to the frequency component and envelope at

the rising point of sound, and this expresses the charac-

teristics of the sound. Therefore, when replaying audio

on audio playback systems, it is extremely important that

the rise section of the signal be expressed accurately

with respect to the original sound.

However, there is inevitable mismatching between the

speakers and amplifiers in current audio systems. Solid-

state power amplifiers use negative feedback techniques

and operate off a fixed voltage supply, but as speakers

are a current element, mismatching in the system inevit-

ably occurs. In addition, the speaker impedance charac-

teristics are strongly influenced by the electrical reac-

tance of the voice coil, and the mechanical reactance of

the cone assembly. As a result of this, distortion is gener-

ated in the rising sections of audio signals, causing

phase shift in the reproduced sound. In addition, imped-

ance increases in the treble region which reduces the

speaker amplitude and reduces the harmonic compo-

nent, and as a result there is a tendency to masking of

large mid-frequency signal components that follow, and

this makes it difficult to reproduce the rising sections of

the sound.

Operating principle

To solve the problems described above, the BA3884F / S

performs the audio signal processing described below.

Phase shift compensation

The input signal is separated into three regions : bass

(20Hz to 150Hz), middle (150Hz to 2.4kHz) and treble

(2.4kHz to 20kHz). These regions are then joined again

with the middle and treble regions phase shifted -180

_

and -360

_ respectively with respect to the bass signal.

This phase shift adjusts the delay time characteristic for

each band and minimizes the distortion of the rising sec-

tion of the audio signal.